Influence of Slenderness on Stress-Strain Behavior of Concrete-Filled FRP Tubes: Experimental Study

Concrete-filled fiber reinforced polymer (FRP) tubes (CFFTs) have received significant research attention over the last two decades, with recent experimental studies identifying significant benefits of CFFTs filled with high-strength concretes (HSC). However, many test parameters of high-strength CFFTs, such as specimen slenderness, remain experimentally limited. This paper presents an experimental investigation on the axial compressive behavior of 33 monotonically loaded circular normal-strength and high-strength CFFTs (NSCFFTs and HSCFFTs). The influence of specimen slenderness is investigated on test specimens with height-to-diameter ratios (H/D) of 1, 2, 3, and 5. The CFFT specimens were instrumented with numerous lateral strain gauges to examine the development of hoop strains along the specimen height and around specimen perimeter. The experimentally recorded stress-strain relationships are presented graphically and the ultimate axial stresses and strains, and FRP tube hoop strains at rupture are tabulated. The results indicate that specimens with a height-to-diameter ratio (H/D) of 1 outperform specimens with a H/D ratio of 2 to 5, with significantly increased strength and strain enhancements. The influence of slenderness on specimens with a H/D ratio between 2 and 5 was found to be significant in regards to axial strain enhancement, with a decrease observed as specimen slenderness increased. Conversely, the influence of slenderness on axial strength enhancement of specimens with a H/D ratio between 2 and 5 was found to be negligible. The strain results indicate that hoop rupture strains along the height of CFFTs become more uniform for specimens with higher amounts of confinement. On the other hand, the variation of hoop strains around the perimeter of CFFTs was not observed to be significantly influenced by slenderness, concrete strength or amount of confinement. (C) 2014 American Society of Civil Engineers.